In recent years, uses of electric products such as audio equipment and a television receiver incorporating a remote control using a remote controller and automatic time control using a timer, have increased. Such electric products commonly have a function that the operation power can be turned on/off by such remote control or automatic time control.
Where the operation power is turned on/off by the remote control or the automatic time control, a supply of standby power is needed to enable the remote control or the automatic time control, even when the operation power is in the off state. Examples of locations to which standby power need to be supplied are a remote controller light receiving section and a control microcomputer.
A power supplying circuit for supplying such standby power has a standby transformer for standby power and a main transformer for operation power. The supply of power to the remote controller light receiving section, the control microcomputer, and so forth is performed by the standby transformer, and the supply of power to a primary power relay during supply of operation power is also performed by the standby transformer. In this type of power supplying circuit, during supply of operation power only the standby transformer supplies power to the remote controller light receiving section, the control microcomputer, and so forth and the primary power relay. The standby transformer is required to have a capacity large enough to supply such power.
For example, a power supplying circuit for remote controller control of audio equipment is required to supply a current of 20 mA to the remote controller light receiving section, the control microcomputer, and so forth. After turning-on of the operation power, a current of 40 mA needs to be supplied to the primary power relay. Therefore, after turning-on of the operation power, a total current of 60 mA flows through the standby transformer. The standby transformer is required to have a rated current of more than 60 mA.
However, there is a problem that, in general, in a transformer having a large rated current, the standby current cannot be made small because of large loss including iron loss and copper loss.
The present invention has been made in view of the above circumstances in the art, and an object of the invention is therefore to provide a power supplying circuit and method that make it possible to use a transformer having a small rated current as a standby transformer.